Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-in HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle- or large-sized devices, such as vehicles, use a middle- or large-sized battery module having a plurality of battery cells electrically connected to one another because high power and large capacity are necessary for the middle- or large-sized devices.
Preferably, the middle- or large-sized battery module is manufactured so as to have a small size and weight if possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle- or large-sized battery module. Especially, considerable interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the weight of the pouch-shaped battery is small, the manufacturing costs of the pouch-shaped battery are low, and it is easy to modify the shape of the pouch-shaped battery.
In order for the middle- or large-sized battery module to provide power and capacity required by a predetermined apparatus or device, it is necessary for the middle- or large-sized battery module to be constructed to have a structure in which a plurality of battery cells are electrically connected in series to one another, and the battery cells are stable against an external force.
Also, the battery cells constituting the middle- or large-sized battery module are secondary batteries which can be charged and discharged. Consequently, a large amount of heat is generated from the high-power, large-capacity secondary batteries during the charge and discharge of the batteries. If the heat, generated from the unit cells during the charge and discharge of the unit cells, is not effectively removed, the heat accumulates in the respective unit cells, with the result that the deterioration of the unit cells is accelerated. According to circumstances, the unit cells may catch fire or explode. For this reason, a cooling system is needed in a battery pack for vehicles, which is a high-power, large-capacity battery, to cool battery cells mounted in the battery pack.
An exemplary cooling system used in a battery pack for vehicles may be constructed to have an air cooling structure. Such an air cooling type cooling system is mainly used in a battery pack for hybrid electric vehicles, having a relatively small amount of heat generated therefrom and assisting driving power.
For a plug-in hybrid electric vehicle, on the other hand, it is necessary for the vehicle to be driven only by power supplied from a battery pack. For this reason, significant electrical load is applied to the battery pack, with the result that a relatively large amount of heat is generated from the battery pack. Consequently, a water cooling type cooling system is mainly applied to the battery pack to protect the battery pack, which is poorly resistant to high temperature.
However, the water cooled type battery pack is considerably different from the air cooled type battery pack in various aspects, such as a battery connection method, a structure in which batteries are stacked in a battery module, a temperature detection method, a voltage measurement method, etc., with the result that it is necessary to additionally develop the battery connection method and the temperature/voltage measurement method.
Consequently, there is a high necessity for a middle- or large-sized battery pack having a novel air cooling structure that is applicable to a battery pack for plug-in hybrid electric vehicles, having a large amount of heat generated therefrom, utilizing the air cooled type battery pack structure for hybrid electric vehicles.